• 한국지하수토양환경학회지:지하수토양환경
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• 제21권6호
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• pp.67-79
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• 2016

Gaussian process regression (GPR) is proposed as a tool of long-term groundwater quality predictions. The major advantage of GPR is that both prediction and the prediction related uncertainty are provided simultaneously. To demonstrate the applicability of the proposed tool, GPR and a conventional non-parametric trend analysis tool are comparatively applied to synthetic examples. From the application, it has been found that GPR shows better performance compared to the conventional method, especially when the groundwater quality data shows typical non-linear trend. The GPR model is further employed to the long-term groundwater quality predictions based on the data from two domestically operated groundwater monitoring stations. From the applications, it has been shown that the model can make reasonable predictions for the majority of the linear trend cases with a few exceptions of severely non-Gaussian data. Furthermore, for the data shows non-linear trend, GPR with mean of second order equation is successfully applied.

• Earthquakes and Structures
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• 제24권6호
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• pp.455-475
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• 2023

The present study investigates the non-linear soil-pile interaction using three-dimensional (3D) non-linear finite element models. The numerical models were validated by using the results of extensive pile load and shaking table tests. The pile performance in liquefiable and non-liquefiable soil has been studied by analyzing the liquefaction ratio, pile lateral displacement (LD), pile bending moment (BM), and frictional resistance (FR) results. The pile models have been developed for the different ground conditions. The study reveals that the results obtained during the pile load test and shaking cycles have good agreement with the predicted pile and soil response. The soil density, peak ground acceleration (PGA), slenderness ratio (L/D), and soil condition (i.e., dry and saturated) are considered during modeling. Four ground motions are used for the non-linear time history analyses. Consequently, design charts are proposed depended on the analysis results to be used for design practice. Eleven models have been used to validate the capability of these charts to capture the soil-pile response under different seismic intensities. The results of the present study demonstrate that L/D ratio slightly affects the lateral displacement when compared with other parameters. Also, it has been observed that the increasing in PGA and decreasing L/D decreases the excess pore water pressure ratio; i.e., increasing PGA from 0.1 g to 0.82 g of loose sand model, decrease the liquefaction ratio by about 50%, and increasing L/D from 15 to 75 of the similar models (under Kobe earthquake), increase this ratio by about 30%. This study reveals that the lateral displacement increases nonlinearly under both dry and saturated conditions as the PGA increases. Similarly, it is observed that the BM increases under both dry and saturated states as the L/D ratio increases. Regarding the acceleration histories, the pile BM was reduced by reducing the acceleration intensity. Hence, the pile BM decreased to about 31% when the applied ground motion switched from Kobe (PGA=0.82 g) to Ali Algharbi (PGA=0.10 g). This study reveals that the soil conditions affect the relationship pattern between the FR and the PGA. Also, this research could be helpful in understanding the threat of earthquakes in different ground characteristics.

• Geomechanics and Engineering
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• 제5권5호
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• pp.379-399
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• 2013

In practice, analysis of laterally loaded piles is carried out using beams on non-linear Winkler springs model (often known as p-y method) due to its simplicity, low computational cost and the ability to model layered soils. In this approach, soil-pile interaction along the depth is characterized by a set of discrete non-linear springs represented by p-y curves where p is the pressure on the soil that causes a relative deformation of y. p-y curves are usually constructed based on semi-empirical correlations. In order to construct API/DNV proposed p-y curve for clay, one needs two values from the monotonic stress-strain test results i.e., undrained strength ($s_u$) and the strain at 50% yield stress (${\varepsilon}_{50}$). This approach may ignore various features for a particular soil which may lead to un-conservative or over-conservative design as not all the data points in the stress-strain relation are used. However, with the increasing ability to simulate soil-structure interaction problems using highly developed computers, the trend has shifted towards a more theoretically sound basis. In this paper, principles of Mobilized Strength Design (MSD) concept is used to construct a continuous p-y curves from experimentally obtained stress-strain relationship of the soil. In the method, the stress-strain graph is scaled by two coefficient $N_C$ (for stress) and $M_C$ (for strain) to obtain the p-y curves. $M_C$ and $N_C$ are derived based on Semi-Analytical Finite Element approach exploiting the axial symmetry where a pile is modelled as a series of embedded discs. An example is considered to show the application of the methodology.

• 한국지반환경공학회 논문집
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• 제19권12호
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• pp.47-58
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• 2018

Duncan & Chang(1970)는 던컨-창 모델을 제안하면서 흙시료의 초기 접선계수와 극한 축차응력을 구하기 위하여 쌍곡선이론을 사용하여 삼축압축시험의 응력-변형률의 비선형관계를 변환된 변형률/축차응력-변형률의 선형관계로 재구성하였다. 그러나 변환된 응력-변형률 관계는 이론적으로 선형관계를 나타내지만, 실제로는 시험이 시작되는 변형률이 작은 구간과 시료가 파괴에 이르는 변형률이 큰 구간에서는 비선형관계를 보인다. 이러한 현상은 삼축압축시험의 응력-변형률 곡선이 완전한 쌍곡선 형태가 아님을 나타낸다. 따라서 변환된 응력-변형률 곡선의 전 구간에 대하여 선형 회귀분석을 실시하여 직선의 식을 구하게 되면, 비선형관계를 나타내는 구간의 범위에 따라 선형관계식의 산정에 편차가 발생하게 된다. 이러한 편차를 줄이기 위하여 본 연구에서는 변환응력-변형률 관계에서 비선형을 나타내는 초반과 종반 구간을 제외한 구간에 대하여 선형회귀분석을 실시함으로써 초기접선계수와 극한 축차응력을 산정하는 수정회귀분석법을 제안하였다. 수정회귀분석법을 검증하기 위하여, 풍화토의 다짐시료에 대하여 압밀-배수 삼축압축시험을 실시하였다. 삼축압축시험의 응력-변형률 곡선으로부터 구한 변환응력-변형률 관계에 대해서 수정회귀분석을 실시하여 Duncan et al.(1980)이 제안한 2점법으로 구한 결과와 비교하였다. 분석결과 수정회기분석법에 비해 Duncan의 2점법으로 산정한 초기 접선계수는 4.0% 크게, 그리고 극한 축차응력은 2.9% 작게 평가되었다.

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 총회 및 춘계학술발표회
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• pp.191-194
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• 2005

Characteristics of sorption and desorption in soils affect chemical fate, soil-remediation time, and selection of remediation technology. The sorption and desorption behavior of atrazine and naphthalene on soils was studied. Six soils collected at Gwangju area were used as sorbents and the organic matter contents ranged from 1.28 to 5.21%. Sorption and desorption experiments were conducted and sorption distribution coefficients(Kd) of atrazine and naphthalene were nearly linear$(R^2=0.93{\sim}0.97)$. Desorption parameters were evaluated using three site desorption model included equilibrium, nonequilibrium and nondesorption sites. Non-desorbable site fraction for atrazine was evaluated, but for naphthalene it was not enumerated during the experimental period. Through the series dilution desorption experiments, non-desorpbable sites were observed for both chemicals.

• Geomechanics and Engineering
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• 제28권2호
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• pp.171-180
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• 2022

Time-dependent stress-strain behaviour significantly influences the compressibility characteristics of the clayey soil. In this paper, a series of oedometer tests were conducted in two loading patterns and investigated the time-dependent compressibility characteristics of Indian Montmorillonite Clay, also known as black cotton soil (BC) soil, during loading-unloading stages. The experimental data are analyzed using a new non-linear function of the Elasto-Visco-Plastic Model considering Swelling behaviour (EVPS model). From the experimental result, it is found that BC soil exhibits significant time-dependent behaviour during creep compared to the swelling stage. Pore water entrance restriction due to consolidated overburden pressure and decrease in cation hydrations are responsible factors. Apart from it, particle sliding is also evident during creep. The time-dependent parameters like strain limit, creep coefficient and C_αe/C_c are observed to be significant during the loading stage than the swelling stage. The relationship between creep coefficients and applied stresses is found to be nonlinear. The creep coefficient increases significantly up to 630 kPa-760 kPa (during reloading), and beyond it, the creep coefficient decreases continuously. Several parameters like loading duration, the magnitude of applied stress, loading history, and loading path have also influenced secondary compressibility characteristics. The time-dependent compressibility characteristics of BC soil are presented and discussed in detail.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.495-508
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• 2010

Vertical drains are commonly used to accelerate the consolidation process of soft soils, such as dredged materials. The installation of vertical drain provides a radial drainage path to water in the deposit soil in addition to the vertical direction. An estimation of time rate of settlement is considerably complicated when vertical drains are installed to enhance consolidation process of dredged material because the vertical drains are commonly installed before self-weight consolidation is ceased. In this paper, the vertical drain theory developed by Barron(1948) is applied to analyze the non-linear consolidation behavior considering radial drainage. The overall average degree of self-weight consolidation of the dredged soil under the condition that the water is drained in both radial and vertical directions is estimated using the Carillo(1942) formula. In addition, the Morris(2002) theory and the one-dimensional non-linear finite strain numerical model, PSDDF, are applied to analyze the self-weight consolidation in case of only the vertical drainage is considered. The new analysis approach proposed herein can simulate properly the time rate of the self-weight consolidation of dredged materials that is facilitated with vertical drains.

• Structural Engineering and Mechanics
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• 제23권3호
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• pp.249-262
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• 2006

In this paper, a simplified mathematical procedure is presented to incorporate nonlinearity in soil material to predict the deceleration time history, penetration depth and other relevant parameters for normal impact of missiles into soil targets. Numerical method is employed for these predictions. The results of the study are compared with experimental observations and predictions available in the literature. A good agreement is found with experimental observations and an improvement is observed with existing predictions. A comparison is also made with linear soil model. Some parametric studies are also carried out to obtain the results of practical interest.

• 산업기술연구
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• 제25권A호
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• pp.57-65
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• 2005

In this paper, for the highly plastic marine soft clay distributed in west and southern coast of Korean peninsula of Kwangyang and Busan New Port areas, correlation between compression index and other indices representing geotechnical engineering properties such as liquid limit, void ratio and natural water content were analyzed. Appropriate empirical equations of being able to estimate the compressibility of clays in the specific areas were proposed and compared with other existing empirical ones. For analyses of the data and test results, data for marine clays were used from areas of the South Container Port of the Busan New Port, East Breakwater, Passenger Quay, Jungma Reclamation and Reclamation Containment in the 3rd stage in Kwangyang. In order to find the best regression model by using the commercially available software, MS EXCEL 2000, results obtained from the simple linear regression analysis, using the values of liquid limit, initial void ratio and natural water content as independent variables, were compared with the existing empirical equations. Multiple linear regression was also performed to find the best fit regression curves for compression index and other soil properties by combining those independent variables. On the other hands, another software of SPSS for non-linear regression was used to analyze the correlations between compression index and other soil properties.

• 한국지반공학회논문집
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• 제28권8호
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• pp.5-19
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• 2012

준설매립지반 설계시 압밀 소요시간 단축을 위해 연직배수공법와 선행재하공법등의 연약지반 개량공법을 주로 적용한다. 준설매립지반의 자중에 의한 압밀이 완료되기까지는 많은 시간이 소요되므로 공사비 절감, 공기단축의 이유로 연약지반 개량공법은 일반적으로 자중압밀 도중 적용된다. 본 논문에서는 준설매립지반에서 연직방향으로 자중압밀이 진행되는 도중 연직배수재 타설에 의해 방사방향의 흐름이 추가로 발생하는 경우의 압밀거동 예측을 위하여 자중압밀을 고려한 2차원 축대칭 비선형 유한변형 압밀 지배방정식과 이를 적용하기 위한 수치모델(Axi-Selcon)을 개발하였다. Axi-Selcon의 검증과 자중압밀 도중 연직배수재가 타설된 준설매립지반을 모사하기 위해 일련의 실내시험을 수행하였다. 이를 위해 연직배수재가 타설된 준설매립지반을 모사하는 대형자중압밀 시험기를 고안하였다. 모델의 추가적인 검증을 위하여 기존에 제안된 간편 해석법을 적용한 결과와 Axi-Selcon의 해석결과와 비교하였다. 마지막으로, Axi-Selcon을 적용하여 가상의 대심도 준설매립지반의 거동을 예측하였다. 이와 같은 일련의 모델 검증과정을 통해 본 논문에서 개발된 Axi-Selcon은 자중압밀 도중 연직배수재 타설과 선행재하공법이 적용될 경우에 대한 초연약 준설매립지반의 압밀 거동을 적절히 예측할 수 있음을 보였다.